QUALITATIVE AND QUANTITATIVE ANALYSIS 61 



Test for Indol : 



Prepare test solutions : 



(a) Paradimethylaminobenzaldehyde 1.0 gm. 



Absolute alcohol 95 . cc. 



Hydrochloric acid (specific gravity 1.2) 20.0 cc. 



(6) Potassium persulphate 1.0 gm. 



Distilled water 100 . cc. 



Place a few drops of solutions (a) and (h) on a piece of absorbent 

 cotton. Push the cotton into the test tube until the moistened 

 surface is within about 1 inch of the culture liquid. Now place 

 the tube in boiling water for 5 to 10 minutes. If indol is present, 

 a red color will appear on the bottom of the cotton plug. 



DETERMINATION OF MOISTURE IN SOIL 



Weigh from 5 to 10 grams of soil into a glass or aluminum 

 dish and dry at 100 to 105°C. until there is no further change in 

 weight. About 6 to 12 hours are generally sufficient. Cool in a 

 desiccator and weigh. Determine all percentages of moisture on 

 the dry basis. 



MOISTURE-HOLDING CAPACITY OF SOIL 



To determine the amount of moisture which is required to 

 saturate the particular soil, the following procedure is used: 

 Round copper cups, about 4 to 5 centimeters in diameter and 

 about 2 centimeters high, with a perforated copper bottom are 

 used. Pieces of filter paper are cut to fit exactly upon the bottom 

 of the cups; the paper is moistened and the cups with the moist- 

 ened paper weighed. The cups are then filled with the soil in 

 question and the surface is leveled off carefully with the edge of 

 the cup. The cups are then weighed again. The cups with soil 

 are now placed in a dish with water, the water reaching out- 

 side of the cup to about half its height. After 24 hours the 

 soil has become saturated with water; the cups are removed and 

 the surface carefully dried with a cloth to remove water adhering 

 to outside of cup, and weighed again. The cups are then placed 

 in a drying oven for 24 hours, at 105°C., until they come to 

 constant weight. The soil is now carefully and completely 

 removed from the cup and from paper, and these weighed again, 

 giving weight of cup and dry paper. The moisture-holding 



